Bill Burton: And it's time for us to take a look at the Science Behind the Forecast as I am joined by WAVE 3 meteorologist Tawana Andrew. Good morning. Tawana.
Tawana Andrew: Good morning. And with all the rain in the forecast this weekend, I figured we'd talk about the smell of the rain.
BB: We're going to learn about the word that describes that smell. And I know it is a word that would have knocked me out of a spelling bee very quickly, because it's not the spelling I would have thought. The word is petrichor. Tell us about it.
TA: Well, honestly, I first learned about this word on a Doctor Who episode. So you're not alone on that.
BB: Doctor Who was such good educational television.
TA: It really is. It really is. But petrichor is the word for the smell of rain. So that earthy smell before it rains. No, you're not losing your mind. That is actually happening. And the term was actually coined by two Australian scientists back in 1964. So petrichor, that earthy smell that comes right before rain, is actually a little bit more noticeable initially, as humidity starts to rise before the rain actually falls. But we get more into it becoming pronounced when the rain actually finally moves into a particular location. So these raindrops are falling on the soil, on the land, on pavement, and they're aerosolizing all of these molecules trapped in these tiny air bubbles on the ground, and the wind is dispersing all of those molecules and that is what we smell. So there are three primary scents associated with petrichor. They're ozone, geosmin, and various plant oils. So the smell of the rain can actually differ depending on what plants are in your area, which is really cool and crazy to think about.
BB: A good excuse to have different plants. I like it.
TA: I like it too. This is why you plant more rose bushes. y'all. So as lightning flashes across the sky, it's basically splitting all of these atoms, which leads to the combination of oxygen molecules, and that creates ozone. And ozone is really mainly discernible after a lightning strike, because that rain is going to bring the ozone from the upper levels of the atmosphere down towards the surface. Now the other thing that we are watching, of course, is going to be bacteria, because in the soil and bodies of water, they produce geosmin and as the raindrops hit the ground, they're throwing those bacteria spores into the air, which, just for note, it's not toxic, so it's not going to get you sick.
BB: Very good to know that it's not going to hurt you.
TA: So that's a good thing to know. And this type of bacteria actually helps organic material decompose. Now, experts suggest that a human can detect geosmin in a concentration as low as 10 nanograms per liter, so it really does not take much for us to smell or even taste it.
BB: An incredibly tiny amount.
TA: In addition to that, rainfall can disperse plant oils. And really, as that rain comes down, you're going to get things like oleic acid and palmitic acid being dispersed by the rain. And this is going to be a little bit more apparent after a long dry spell. So these oils are primarily from plant leaves, and they accumulate in the soil or on pavement during dry weather, and then the rainfall will release them into the atmosphere. And experts believe that these oils actually inhibit seed germination, which reduces competition for much needed water when we're in a really long dry spell. So it's doing kind of double duty there.
BB: So there's a lot to understand when it comes to petrichor. P-E-T-R-I-C-H-O-R. Maybe I would have won the spelling bee. But now we have a much better understanding of this thanks to this edition of Science Behind the Forecast. Thanks for the knowledge. Tawana.
TA: Of course.
This transcript was edited for clarity.
